scholarly journals Phases and Phase Transitions in the First Few Layers of Methane, Argon and Krypton Adsorbed on Graphite

1992 ◽  
Vol 280 ◽  
Author(s):  
David Goodstein ◽  
P. Day ◽  
M. LaMadrid ◽  
M. Lysek
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Capillary Condensation ◽  
Equilibrium Phase ◽  
Scanning Calorimetry ◽  
Liquid Phases ◽  
Thermodynamic Measurements ◽  
Solid Phases ◽  
Liquid And Solid Phases

ABSTRACTThe equilibrium phase diagrams of monolayers of many substances adsorbed on graphite have long been studied as examples of 2-dimensional (2D) matter. One typically observes 2D gas and liquid phases, and solid phases that may be commensurate or incommensurate with the substrate lattice. Many experimental techniques have been used, but thermodynamic measurements are generally the most useful for tracing out phase boundaries.Recent advances in technique have made it possible to use thermodynamic measurements to study the phase diagrams of the second and higher layers, up to the fifth or sixth. These advances include ultra high resolution scanning calorimetry, and a detailed understanding of the role of capillary condensation in corners and pores of the graphite foam substrate. We find a rich array of phases and phase transitions in multilayer methane, argon and krypton. The second and third layers typically have distinct 2D gas, liquid and solid phases evidenced by 2D triple points and critical points. We observe phase transitions between solid phases that are commensurate and incommensurate with the layer below. We also observe melting of the first layer at higher temperatures, even when one to five additional layers are adsorbed on top of it.In argon and krypton, but not in methane, a strange new phenomenon is observed at temperatures above the gas-liquid critical point of the nth layer for n> 3. Below that temperature, nthlayer gas coexists with a condensed nth layer. At some temperature above it, a new coexistence region is observed in which a partial nth layer coexists with a partial n + 1st layer. This behavior is thought to be evidence for a theoretically predicted phase transition of the bulk interface, called the preroughening transition.

scholarly journals Double-Chain Cationic Surfactants: Swelling, Structure, Phase Transitions and Additive Effects

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3946
Author(s):  
Rui A. Gonçalves ◽  
Yeng-Ming Lam ◽  
Björn Lindman
Keyword(s):  
Phase Transitions ◽  
Phase Behaviour ◽  
Double Chain ◽  
Scanning Calorimetry ◽  
Alkyl Chains ◽  
X Ray Scattering ◽  
Amphiphilic Compounds ◽  
Liquid Phases ◽  
Lamellar Phases ◽  
Water Layers

Double-chain amphiphilic compounds, including surfactants and lipids, have broad significance in applications like personal care and biology. A study on the phase structures and their transitions focusing on dioctadecyldimethylammonium chloride (DODAC), used inter alia in hair conditioners, is presented. The phase behaviour is dominated by two bilayer lamellar phases, Lβ and Lα, with “solid” and “melted” alkyl chains, respectively. In particular, the study is focused on the effect of additives of different polarity on the phase transitions and structures. The main techniques used for investigation were differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). From the WAXS reflections, the distance between the alkyl chains in the bilayers was obtained, and from SAXS, the thicknesses of the surfactant and water layers. The Lα phase was found to have a bilayer structure, generally found for most surfactants; a Lβ phase made up of bilayers with considerable chain tilting and interdigitation was also identified. Depending mainly on the polarity of the additives, their effects on the phase stabilities and structure vary. Compounds like urea have no significant effect, while fatty acids and fatty alcohols have significant effects, but which are quite different depending on the nonpolar part. In most cases, Lβ and Lα phases exist over wide composition ranges; certain additives induce transitions to other phases, which include cubic, reversed hexagonal liquid crystals and bicontinuous liquid phases. For a system containing additives, which induce a significant lowering of the Lβ–Lα transition, we identified the possibility of a triggered phase transition via dilution with water.

scholarly journals Phase Polymorphism of [Co(DMSO)6](BF4)2 Studied by Differential Scanning Calorimetry

2006 ◽  
Vol 61 (3-4) ◽  
pp. 180-188 ◽  
Author(s):  
Anna Migdał-Mikuli ◽  
Łukasz Skoczylas ◽  
Elżbieta Szostak
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Melting Point ◽  
Title Compound ◽  
Metastable Phases ◽  
Scanning Calorimetry ◽  
Phase Polymorphism ◽  
Solid Phases ◽  
High Degree ◽  
Dynamical Disorder

Five solid phases of [Co(DMSO)6](BF4)2 have been detected by differential scanning calorimetry (DSC). Phase transitions were detected between the following solid phases: stable KIb↔ stable KIa at T̅C4 = (328±2) K, metastable KIII ↔ undercooled phase K0 at T̅C3 = (383±4) K, metastable KII ↔ undercooled K0 at T̅C2 = (399±2) K and stable KIa ↔ stable K0 at T̅C1 = (404±1) K. The title compound melts at Tm = 440 K. From the entropy changes at the melting point and at phase transitions it can be concluded that the phases K0 and undercooled K0 are orientationally dynamically disordered crystals. The stable phases KIa, KIb are ordered solid phases. The metastable phases KII and KIII are probably solid phases with a high degree of orientational dynamical disorder

scholarly journals Phase Transitions of Binary Lipid Mixtures: A Combined Study by Adiabatic Scanning Calorimetry and Quartz Crystal Microbalance with Dissipation Monitoring

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
P. Losada-Pérez ◽  
N. Mertens ◽  
B. de Medio-Vasconcelos ◽  
E. Slenders ◽  
J. Leys ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Quartz Crystal Microbalance ◽  
Quartz Crystal ◽  
Phase Behaviour ◽  
Scanning Calorimetry ◽  
Departure Point ◽  
Peltier Element ◽  
Adiabatic Scanning Calorimetry ◽  
Lipid Mixtures

The phase transitions of binary lipid mixtures are studied by a combination of Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D). pASC, a novel type of calorimeter, provides valuable and unambiguous information on the heat capacity and the enthalpy, whereas QCM-D is proposed as a genuine way of determining phase diagrams by analysing the temperature dependence of the viscosity. Two binary mixtures of phospholipids with the same polar head and differing in the alkyl chain length, DMPC + DPPC and DMPC + DSPC, are discussed. Both techniques give consistent phase diagrams, which compare well with literature results, showing their capability to map the phase behaviour of pure lipids as well as lipid mixtures. This work can be considered as a departure point for further investigations on more complex lipid mixtures displaying relevant phases such as the liquid-ordered phase and solid-lipid interfaces with biologically functional importance.

Accurate Calculation of the Non-Variant Points of Equilibrium Phase Diagrams by Using the ESTPHAD Method

2012 ◽  
Vol 729 ◽  
pp. 448-454 ◽  
Author(s):  
Tamás Mende ◽  
András Roósz
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Equilibrium Phase ◽  
High Accuracy ◽  
Exact Calculation ◽  
Accurate Calculation

Certain phase transitions take place at a given temperature in the equilibrium phase diagrams, the values of their temperatures can exactly be measured so it is an essential task to calculate these values by a high accuracy. New parameters were introduced into the ESTPHAD equation for calculating the so-called non-variant points. By using the ESTPHAD method, the accuracy of calculations are compared to the data used for the calculations so the exact calculation of the temperatures of non-variant points are defined as compared to the data used for the calculations.

scholarly journals Application of equilibrium phase diagrams for calculation of segregation kinetics during two-component melt cooling

2020 ◽  
Vol 63 (2) ◽  
pp. 129-134
Author(s):  
A. D. Drozin ◽  
E. Yu. Kurkina
Keyword(s):  
Liquid Phase ◽  
Equilibrium State ◽  
Cross Section ◽  
Diffusion Coefficients ◽  
Solid Phase ◽  
Equilibrium Phase ◽  
Minimum Size ◽  
Two Component ◽  
Solid Phases ◽  
Liquid And Solid Phases

According to the equilibrium state diagrams, when the melt is cooled to a certain temperature below liquidus, compositions of liquid and solid phases are uniquely determined by corresponding curves in the diagram. However, it does not happen in reality. For equilibrium (which the diagram describes), it is necessary that the melt is maintained indefinitely at each temperature, or thermal conductivity of liquid and solid phases, and the diffusion coefficients of their components, are infinitely large. We made an attempt to find out how these processes occur in reality. In this work, we consider the growth of individual crystal during cooling of a two-component melt. Mathematical model is constructed based on the following. 1. The melt area with volume corresponding to one grain, the periphery of which is cooled according to a certain law, is considered. 2. At the initial instant of time, a crystal nucleus of a certain minimum size is in the liquid. 3. At the surface of crystal, compositions of liquid and solid phases correspond to equilibrium state diagram at a given temperature on its surface. 4. Changes in temperature and composition in liquid and solid phases occur according to the laws of heat conduction and diffusion, respectively. As the melt gets cold and the crystal grows, the liquid phase is enriched in one component and depleted in another, the solid phase – on the contrary. Since the diffusion coefficients of the components in the solid phase are small, the composition of the crystal does not have time to completely equalize its cross section. The model proposed in the work allows us to study this phenomenon, to calculate for each cooling mode how the composition of the crystal will vary over its cross section. The calculations have shown that the temperature equalization occurs almost instantly, and composition of the liquid phase equalizes much slower. Equalization of the solid phase composition does not occur in the foreseeable time. The results of the work will help to improve technology of generation of alloys with an optimal structure.

scholarly journals Formation of Interfacial Reaction Layers in Al2O3/SS 430 Brazed Joints Using Cu-7Al-3.5Zr Alloys

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 990 ◽  
Author(s):  
Hoejun Heo ◽  
Hyeonim Joung ◽  
Keeyoung Jung ◽  
Chung-Yun Kang
Keyword(s):  
Liquid Phase ◽  
Interfacial Reaction ◽  
Eutectic Temperature ◽  
Liquid Phases ◽  
430 Stainless Steel ◽  
Brazed Joints ◽  
Solid Phases ◽  
Α Al2o3 ◽  
Kinetics Of ◽  
Liquid And Solid Phases

The formation of interfacial reaction layers was investigated in an α-Al2O3/430 stainless steel (SS430) joint brazed using a Cu-7Al-3.5Zr active brazing alloy. Brazing was conducted at above its eutectic temperature of 945 °C and below liquidus 1045 °C, where liquid and solid phases of the brazing alloys coexists. At 1000 °C, the liquid phase of the brazing alloy was wet onto the α-Al2O3 surface. Zr in the liquid phase reduced α-Al2O3 to form a continuous ZrO2 layer. As the dwell time increased, Zr in the liquid phases near α-Al2O3 interface was used up to thicken the reaction layers. The growth kinetics of the layer obeys the parabolic rate law with a rate constant of 9.25 × 10−6 cm·s−1/2. It was observed that a number of low yield strength Cu-rich particles were dispersed over the reaction layer, which can release the residual stress of the joint resulting in reduction of crack occurrence.

Thermodynamics of Te80Ge20 − x Pbx glass-forming alloys

1988 ◽  
Vol 3 (3) ◽  
pp. 570-575 ◽  
Author(s):  
L. Battezzati ◽  
A. L. Greer
Keyword(s):  
Free Energy ◽  
Specific Heat ◽  
Glass Forming Ability ◽  
Undercooled Liquid ◽  
Scanning Calorimetry ◽  
Entropy Of Fusion ◽  
Glass Forming ◽  
Crystal Phases ◽  
Solid Phases ◽  
Liquid And Solid Phases

The specific heat of liquid and solid phases and the heats of crystallization and fusion have been measured by differential scanning calorimetry (DSC) for a series of Te80Ge20 − x Pbx alloys (0≤x≤20). The enthalpy, entropy, and free energy of the undercooled liquid are quantitatively assessed with reference to the crystal phases. The available formulas for computing the free energy of the liquid are compared, and their relative merits are discussed. The glass transition temperature is shown to depend strongly on the ratio of the average excess specific heat of the liquid to the entropy of fusion. An anomaly in the liquid specific heat, which is particularly important for Te80Ge20 and Te80Ge15Pb5, leads to very good glass forming ability for these alloys; this is demonstrated by preparing amorphous samples by means of fluxing.

scholarly journals Phase Polymorphism of [Mn(DMSO)6](BF4)2 Studied by Differential Scanning Calorimetry

2008 ◽  
Vol 63 (12) ◽  
pp. 808-812 ◽  
Author(s):  
Anna Migdał-Mikuli ◽  
Łukasz Skoczylas
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Dmso Molecule ◽  
Formula Unit ◽  
Scanning Calorimetry ◽  
First Order ◽  
Temperature Range ◽  
Phase Polymorphism ◽  
One Step ◽  
Solid Phases

The tetrafluoroborate of hexadimethylsulfoxidemanganese(II) was synthesized and studied by differential scanning calorimetry. Five solid phases of [Mn(DMSO)6](BF4)2 were revealed. Specifically, four phase transitions of the first order were detected between the following solid phases: stable KIb↔stable KIa at TC4 = 215 K; metastable KIII↔overcooled K0 at TC3 = 354 K; metastable KII↔overcooled K0 at TC2 =377 K; stable KIa→stable K0 at TC1 =385 K. [Mn(DMSO)6](BF4)2 starts to decompose at 400 K with a loss of one DMSO molecule per formula unit and forms [Mn(DMSO)5](BF4)2 which next decomposes in one step to MnF2 at the temperature range of 460 - 583 K. From the entropy changes it can be concluded that the phases K0 and metastable KII are orientationally dynamically disordered (ODDIC) crystals. The stable phases KIb and KIa are ordered solid phases.

Calculation of Gallium-Arsenic-Metal Phase Diagrams

1990 ◽  
Vol 204 ◽  
Author(s):  
James D. Scofield ◽  
J. E. Davison ◽  
S. R. Smith
Keyword(s):  
Free Energy ◽  
Phase Diagrams ◽  
Ternary Alloy ◽  
Regular Solution ◽  
Alloy System ◽  
Energy Functions ◽  
Solid Phases ◽  
Solution Parameters ◽  
Liquid And Solid Phases ◽  
Alloy Systems

ABSTRACTContact metallizations for space-based GaAs solar cells must survive at high temperatures for several minutes. Which metallizations will survive can be predicted by properly calculated phase diagrams instead of performing hundreds of reactions. A method for calculating the ternary temperature constitution phase diagrams Is briefly explained and the phase diagrams are calculated for two Ga-As-X alloy systems. The free energy functions of the liquid and solid phases are approximated by the regular solution theory. The phase diagrams of the three binary alloy systems which form the boundaries of the ternary alloy system are utilized to calculate the binary regular solution parameters. The free energy functions for the ternary liquid and solid phases are expressed In terms of the binary regular solution parameters. The temperature and composition of the liquidus and solidus boundaries for the ternary alloy systems are calculated from these free energy functions. Calculated results are presented for the Ga-As-Ag and the Ga-As-Ge systems.

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